Spatial modulation-based groupings for device power savings

ABSTRACT

In one embodiment, a device in a network receives, at its wireless receiver, a preamble of a spatially modulated packet. The device analyzes the preamble of the packet to identify a transmit antenna index of the packet. The device determines that the packet was not destined for the device, based on the transmit antenna index of the packet. The device depowers, prior to decoding the complete packet, the wireless receiver of the device, based on the determination that the packet was not destined for the device.

TECHNICAL FIELD

The present disclosure relates generally to computer networks, and, moreparticularly, to spatial modulation-based device groupings.

BACKGROUND

The Internet of Things, or “IoT” for short, represents an evolution ofcomputer networks that seeks to connect many everyday objects to theInternet. Notably, there has been a recent proliferation of “smart”devices that are Internet-capable such as thermostats, lighting,televisions, cameras, and the like. In many implementations, thesedevices may also communicate with one another. For example, an IoTmotion sensor may communicate with one or more smart lightbulbs, toactuate the lighting in a room, when a person enters the room.

In contrast to many traditional computer networks, various challengesare presented with IoT devices, such as lossy links, low bandwidth,battery operation, low memory and/or processing capability of thedevice, etc. Changing environmental conditions may also affect devicecommunications. For example, physical obstructions (e.g., changes in thefoliage density of nearby trees, the opening and closing of doors,etc.), changes in interference (e.g., from other wireless networks ordevices), propagation characteristics of the media (e.g., temperature orhumidity changes, etc.), and the like, also present unique challenges tothe IoT.

As noted, most IoT devices are battery powered, making low-poweroperations indispensable, as there exists a tradeoff between latency andbattery life. To extend the battery life of an IoT device, many deviceswill periodically enter into a sleep mode. Thus, if an IoT devicerequires lower latency and higher responsiveness, it must be awake andavailable on the wireless network more frequently, which significantlyreduces its battery life. One key observation is that an awake IoTdevice will spend a large amount of resources processing the mediaaccess control (MAC) headers of all packets that it receives, even forones that are not destined/intended for the IoT device. As introducedherein, reducing this packet processing through the use of spatialmodulation-based device groupings can help to increase the battery lifeof an IoT device, considerably.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein may be better understood by referring to thefollowing description in conjunction with the accompanying drawings inwhich like reference numerals indicate identically or functionallysimilar elements, of which:

FIG. 1 illustrate an example computer network;

FIG. 2 illustrates an example network device/node;

FIG. 3 illustrates an example wireless network;

FIG. 4 illustrates an example of using spatial modulation for groupingwireless devices;

FIG. 5 illustrates an example of a wireless device processing aspatially modulated packet;

FIGS. 6A-6B illustrate examples of wireless devices estimating thechannel of spatially modulated packets; and

FIG. 7 illustrates an example simplified procedure for using spatialmodulation for power savings.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

According to one or more embodiments of the disclosure, a device in anetwork receives, at its wireless receiver, a preamble of a spatiallymodulated packet. The device analyzes the preamble of the packet toidentify a transmit antenna index of the packet. The device determinesthat the packet was not destined for the device, based on the transmitantenna index of the packet. The device depowers, prior to decoding thecomplete packet, the wireless receiver of the device, based on thedetermination that the packet was not destined for the device.

DESCRIPTION

A computer network is a geographically distributed collection of nodesinterconnected by communication links and segments for transporting databetween end nodes, such as personal computers and workstations, or otherdevices, such as sensors, etc. Many types of networks are available,ranging from local area networks (LANs) to wide area networks (WANs).LANs typically connect the nodes over dedicated private communicationslinks located in the same general physical location, such as a buildingor campus. WANs, on the other hand, typically connect geographicallydispersed nodes over long-distance communications links, such as commoncarrier telephone lines, optical lightpaths, synchronous opticalnetworks (SONET), synchronous digital hierarchy (SDH) links, orPowerline Communications (PLC), and others. Other types of networks,such as field area networks (FANs), neighborhood area networks (NANs),personal area networks (PANs), etc. may also make up the components ofany given computer network.

In various embodiments, computer networks may include an Internet ofThings network. Loosely, the term “Internet of Things” or “IoT” (or“Internet of Everything” or “IoE”) refers to uniquely identifiableobjects (things) and their virtual representations in a network-basedarchitecture. In particular, the IoT involves the ability to connectmore than just computers and communications devices, but rather theability to connect “objects” in general, such as lights, appliances,vehicles, heating, ventilating, and air-conditioning (HVAC), windows andwindow shades and blinds, doors, locks, etc. The “Internet of Things”thus generally refers to the interconnection of objects (e.g., smartobjects), such as sensors and actuators, over a computer network (e.g.,via IP), which may be the public Internet or a private network.

Often, IoT networks operate within a shared-media mesh networks, such aswireless or PLC networks, etc., and are often on what is referred to asLow-Power and Lossy Networks (LLNs), which are a class of network inwhich both the routers and their interconnect are constrained. That is,LLN devices/routers typically operate with constraints, e.g., processingpower, memory, and/or energy (battery), and their interconnects arecharacterized by, illustratively, high loss rates, low data rates,and/or instability. IoT networks are comprised of anything from a fewdozen to thousands or even millions of devices, and supportpoint-to-point traffic (between devices inside the network),point-to-multipoint traffic (from a central control point such as a rootnode to a subset of devices inside the network), and multipoint-to-pointtraffic (from devices inside the network towards a central controlpoint).

Fog computing is a distributed approach of cloud implementation thatacts as an intermediate layer from local networks (e.g., IoT networks)to the cloud (e.g., centralized and/or shared resources, as will beunderstood by those skilled in the art). That is, generally, fogcomputing entails using devices at the network edge to provideapplication services, including computation, networking, and storage, tothe local nodes in the network, in contrast to cloud-based approachesthat rely on remote data centers/cloud environments for the services. Tothis end, a fog node is a functional node that is deployed close to fogendpoints to provide computing, storage, and networking resources andservices. Multiple fog nodes organized or configured together form a fogsystem, to implement a particular solution. Fog nodes and fog systemscan have the same or complementary capabilities, in variousimplementations. That is, each individual fog node does not have toimplement the entire spectrum of capabilities. Instead, the fogcapabilities may be distributed across multiple fog nodes and systems,which may collaborate to help each other to provide the desiredservices. In other words, a fog system can include any number ofvirtualized services and/or data stores that are spread across thedistributed fog nodes. This may include a master-slave configuration,publish-subscribe configuration, or peer-to-peer configuration.

Low power and Lossy Networks (LLNs), e.g., certain sensor networks, maybe used in a myriad of applications such as for “Smart Grid” and “SmartCities.” A number of challenges in LLNs have been presented, such as:

1) Links are generally lossy, such that a Packet Delivery Rate/Ratio(PDR) can dramatically vary due to various sources of interferences,e.g., considerably affecting the bit error rate (BER);

2) Links are generally low bandwidth, such that control plane trafficmust generally be bounded and negligible compared to the low rate datatraffic;

3) There are a number of use cases that require specifying a set of linkand node metrics, some of them being dynamic, thus requiring specificsmoothing functions to avoid routing instability, considerably drainingbandwidth and energy;

4) Constraint-routing may be required by some applications, e.g., toestablish routing paths that will avoid non-encrypted links, nodesrunning low on energy, etc.;

5) Scale of the networks may become very large, e.g., on the order ofseveral thousands to millions of nodes; and

6) Nodes may be constrained with a low memory, a reduced processingcapability, a low power supply (e.g., battery).

In other words, LLNs are a class of network in which both the routersand their interconnect are constrained: LLN routers typically operatewith constraints, e.g., processing power, memory, and/or energy(battery), and their interconnects are characterized by, illustratively,high loss rates, low data rates, and/or instability. LLNs are comprisedof anything from a few dozen and up to thousands or even millions of LLNrouters, and support point-to-point traffic (between devices inside theLLN), point-to-multipoint traffic (from a central control point to asubset of devices inside the LLN) and multipoint-to-point traffic (fromdevices inside the LLN towards a central control point).

An example implementation of LLNs is an “Internet of Things” network.Loosely, the term “Internet of Things” or “IoT” may be used by those inthe art to refer to uniquely identifiable objects (things) and theirvirtual representations in a network-based architecture. In particular,the next frontier in the evolution of the Internet is the ability toconnect more than just computers and communications devices, but ratherthe ability to connect “objects” in general, such as lights, appliances,vehicles, HVAC (heating, ventilating, and air-conditioning), windows andwindow shades and blinds, doors, locks, etc. The “Internet of Things”thus generally refers to the interconnection of objects (e.g., smartobjects), such as sensors and actuators, over a computer network (e.g.,IP), which may be the Public Internet or a private network. Such deviceshave been used in the industry for decades, usually in the form ofnon-IP or proprietary protocols that are connected to IP networks by wayof protocol translation gateways. With the emergence of a myriad ofapplications, such as the smart grid advanced metering infrastructure(AMI), smart cities, and building and industrial automation, and cars(e.g., that can interconnect millions of objects for sensing things likepower quality, tire pressure, and temperature and that can actuateengines and lights), it has been of the utmost importance to extend theIP protocol suite for these networks.

FIG. 1 is a schematic block diagram of an example simplified computernetwork 100 illustratively comprising nodes/devices at various levels ofthe network, interconnected by various methods of communication. Forinstance, the links may be wired links or shared media (e.g., wirelesslinks, PLC links, etc.) where certain nodes, such as, e.g., routers,sensors, computers, etc., may be in communication with other devices,e.g., based on connectivity, distance, signal strength, currentoperational status, location, etc.

Specifically, as shown in the example network 100, three illustrativelayers are shown, namely the cloud 110, fog 120, and IoT device 130.Illustratively, the cloud 110 may comprise general connectivity via theInternet 112, and may contain one or more datacenters 114 with one ormore centralized servers 116 or other devices, as will be appreciated bythose skilled in the art. Within the fog layer 120, various fognodes/devices 122 (e.g., with fog modules, described below) may executevarious fog computing resources on network edge devices, as opposed todatacenter/cloud-based servers or on the endpoint nodes 132 themselvesof the IoT layer 130. Data packets (e.g., traffic and/or messages sentbetween the devices/nodes) may be exchanged among the nodes/devices ofthe computer network 100 using predefined network communicationprotocols such as certain known wired protocols, wireless protocols, PLCprotocols, or other shared-media protocols where appropriate. In thiscontext, a protocol consists of a set of rules defining how the nodesinteract with each other.

Those skilled in the art will understand that any number of nodes,devices, links, etc. may be used in the computer network, and that theview shown herein is for simplicity. Also, those skilled in the art willfurther understand that while the network is shown in a certainorientation, the network 100 is merely an example illustration that isnot meant to limit the disclosure.

Data packets (e.g., traffic and/or messages) may be exchanged among thenodes/devices of the computer network 100 using predefined networkcommunication protocols such as certain known wired protocols, wirelessprotocols (e.g., IEEE Std. 802.15.4, Wi-Fi, Bluetooth®, DECT-Ultra LowEnergy, LoRa, etc.), PLC protocols, or other shared-media protocolswhere appropriate. In this context, a protocol consists of a set ofrules defining how the nodes interact with each other.

FIG. 2 is a schematic block diagram of an example node/device 200 thatmay be used with one or more embodiments described herein, e.g., as anyof the nodes or devices shown in FIG. 1 above or described in furtherdetail below. The device 200 may comprise one or more network interfaces210 (e.g., wired, wireless, PLC, etc.), at least one processor 220, anda memory 240 interconnected by a system bus 250, as well as a powersupply 260 (e.g., battery, plug-in, etc.).

The network interface(s) 210 include the mechanical, electrical, andsignaling circuitry for communicating data to and/or from a network. Forexample, network interface(s) 210 may include a wireless receiver,transmitter, or both (e.g., a transceiver).

The memory 240 comprises a plurality of storage locations that areaddressable by the processor 220 and the network interfaces 210 forstoring software programs and data structures associated with theembodiments described herein. Note that certain devices may have limitedmemory or no memory (e.g., no memory for storage other than forprograms/processes operating on the device and associated caches). Theprocessor 220 may comprise hardware elements or hardware logic adaptedto execute the software programs and manipulate the data structures 245.Operating system 242, portions of which is typically resident in memory240 and executed by the processor, functionally organizes the device by,inter alia, invoking operations in support of software processes and/orservices executing on the device. These software processes and/orservices may comprise a communication process 248, as described herein.

It will be apparent to those skilled in the art that other processor andmemory types, including various computer-readable media, may be used tostore and execute program instructions pertaining to the techniquesdescribed herein. Also, while the description illustrates variousprocesses, it is expressly contemplated that various processes may beembodied as modules configured to operate in accordance with thetechniques herein (e.g., according to the functionality of a similarprocess). Further, while the processes have been shown separately, thoseskilled in the art will appreciate that processes may be routines ormodules within other processes.

FIG. 3 illustrates an example wireless network 300, according to variousembodiments. Wireless network 300 may be deployed to a physicallocation, such as floor 302 shown, and may include variousinfrastructure devices. These infrastructure devices may include, forexample, one or more access points (APs) 304 that provide wirelessconnectivity to the various wireless clients 306 distributed throughoutthe location. For illustrative purposes, APs 304 a-304 d and clients 306a-306 i are depicted in FIG. 3. However, as would be appreciated, awireless network deployment may include any number of APs and clients.

A network backbone 310 may interconnect APs 304 and provide a connectionbetween APs 304 and any number of supervisory devices or services thatprovide control over APs 304. For example, as shown, a wireless LANcontroller (WLC) 312 may control some or all of APs 304 a-404 d, bysetting their control parameters (e.g., max number of attached clients,channels used, wireless modes, etc.). Another supervisory service thatoversees wireless network 300 may be a monitoring and analytics service314 that measures and monitors the performance of wireless network 300and, if so configured, may also adjust the operation of wireless network300 based on the monitored performance (e.g., via WLC 312, etc.). Notethat service 314 may be implemented directly on WLC 312 or may operatein conjunction therewith, in various implementations.

Network backbone 310 may further provide connectivity between theinfrastructure of the local network and a larger network, such as theInternet, a Multiprotocol Label Switching (MPLS) network, or the like.Accordingly, WLC 312 and/or monitoring and analytics service 314 may belocated on the same local network as APs 304 or, alternatively, may belocated remotely, such as in a remote datacenter, in the cloud, etc. Toprovide such connectivity, network backbone 310 may include any numberof wired connections (e.g., Ethernet, optical, etc.) and/or wirelessconnections (e.g., cellular, etc.), as well as any number of networkingdevices (e.g., routers, switches, etc.).

The types and configurations of clients 304 in network 300 can varygreatly and include any number of different types of IoT nodes/devices.For example, clients 306 a-306 c may be mobile phones, clients 306 d-306f may be office phones, and clients 306 g-306 i may be computers, all ofwhich may be of different makes, models, and/or configurations (e.g.,firmware or software versions, chipsets, etc.). Further examples ofclients 306 can include, but are not limited to, wireless sensors,actuators, thermostats, relays, and the like.

As noted above, power operation is an indispensable feature in many IoTdevices. To account for the tradeoff between latency and battery life,various approaches have been proposed. For example, one proposal underthe 802.11 protocol is to implement a Power Save Mode (PSM) in which thewireless client (STA) can sleep when data is not being communicated.However, with this duty-cycled operation, low power consumption and lowlatency are conflicting goals. In order to increase battery life, adevice needs to sleep more often, which causes increased latency incommunications with the device. To receive data with low latency, adevice needs to sleep less frequently, which causes shorter batterylife. So, the ultimate goal is to provide a solution that consumes lesspower, while keeping the IoT devices more responsive with low latency.

Even when subjecting an IoT device to sleep cycles to decrease batteryconsumption, there is still a considerable amount of unnecessaryprocessing by the device that still consumes power. For example, in itsawake mode, a typical IoT device will need to decode all media accesscontrol (MAC) headers of its received packets, to identify and extractthe payloads of the packets that are actually intended/destined for thedevice.

Spatial Modulation-Based Groupings for Device Power Savings

The techniques herein introduce a power saving approach for wirelessdevices that relies on spatial modulation to group devices according tothe antenna index of the sender. In doing so, a receiving device canquickly filter out packets not intended/destined for the device by onlyprocessing the preamble of the packets, as opposed to its full MACheader, reducing power consumption by the device.

Specifically, according to one or more embodiments of the disclosure asdescribed in detail below, a device in a network receives, at itswireless receiver, a preamble of a spatially modulated packet. Thedevice analyzes the preamble of the packet to identify a transmitantenna index of the packet. The device determines that the packet wasnot destined for the device, based on the transmit antenna index of thepacket. The device depowers, prior to decoding the complete packet, thewireless receiver of the device, based on the determination that thepacket was not destined for the device.

Illustratively, the techniques described herein may be performed byhardware, software, and/or firmware, such as in accordance with thecommunication process 248, which may include computer executableinstructions executed by the processor 220 (or independent processor ofinterfaces 210) to perform functions relating to the techniquesdescribed herein.

Operationally, the techniques herein provide for device power savings byleveraging the preamble of a wireless packet in which theAmplitude-Phase Modulation (APM) domain is known to the receiving deviceand device group numbers are conveyed via the spatial domain of thepacket. In various embodiments, the receiving device can identify themulticast address of the packet (e.g., the group number) by detectingthe antenna index of transmitter. If the group number does not matchthat of the device, the device may skip decoding the rest of the packetand turn off its radio to save power.

According to various embodiments, the techniques herein introduce aflexible framework that can work on top of other power saving mechanismssuch as a legacy power management policy, Target Wake Time (TWT), and802.11ba wake-up radio, to conserve even more power by depowering theradio and stopping further decoding of the packet after decoding thelegacy signal (L-SIG) field of the packet. For example, in someembodiments, the device may determine a spatial multicast address of thepacket by estimating the channel used from the legacy long trainingfield (L-LTF) of the packet. This allows the device to quickly determinewhether the packet is intended/destined for the device. In addition, thetechniques herein can be implemented without requiring any additionalradios on the sender or receiver.

In general, spatial modulation is a multiple-antenna transmissiontechnique that uses antenna indexes as an additional means of datatransmissions. In this scheme, a spatial modulation symbol, whichconsists of multiple bits, is transmitted over two domains:

1.) The Amplitude-Phase Modulation (APM) Domain—this can take the formof any conventional digital modulation such as, but not limited to,binary phase shift keying (BPSK), quadrature phase shift keying (QPSK),cross quadrature amplitude modulation (xQAM), and the like.

2.) The Spatial Domain—this can be utilized by assigning the index ofactive transmit antenna to each symbol.

As would be appreciated, spatial modulation can offer improved datarates compared to Single-Input Single-Output (SISO) systems, and offersrobust performance, in terms of bit and packet error rates, even incorrelated channel environments. In a typical embodiment of spatialmodulation, only the receiver requires the Channel State Information(CSI) from each transmit antenna and CSI is not required at transmitter.

FIG. 4 illustrates an example 400 of using spatial modulation forgrouping wireless devices, according to various embodiments. As shown,assume that an AP 304 includes a plurality of transmit (Tx) antennas 410a-410 d to communicate with a plurality of clients 306 (e.g., IoT orother wireless devices).

In various embodiments, AP 304 may maintain a set of device groupassignments 402 that group clients 306 into various groupings 414 a-414d, which effectively serve as different multicast groups within thenetwork. In turn, AP 304 may use spatial modulation to indicate which ofgroupings 414 a-414 d is the intended destination of the packet. Aswould be appreciated, the key idea behind spatial modulation is to usethe index of the active antennas 410 at any time instant, to conveyextra information with the packet.

To spatially modulate a packet, AP 304 may include a basebandtransmitter 404 that always uses a single transmit RF chain 406 andcontrols an RF switch 408 to select which of transmit antennas 410 a-410d is used to convey the packet. The index of the transmit antenna isunchanged during packet transmission and AP 304 may apply the selectedgroup number assignment 402 on the packet after RF chain 406 and RFswitch 408 select the antenna 410 corresponding to the group number. Forexample, the index of transmit antenna 410 a may correspond to the groupnumber of device grouping 414 a in group assignments 402, the index oftransmit antenna 410 b may correspond to the group number of devicegrouping 414 b in group assignments 402, the index of transmit antenna410 c may correspond to the group number of device grouping 414 c ingroup assignments 402, and the index of transmit antenna 410 d maycorrespond to the group number of device grouping 414 d in groupassignments 402. Thus, when a client device 306 receives the packet, itcan quickly assess the group number/antenna index of the packet, todetermine whether the packet was intended/destined for the client,without having to decode the entire packet.

FIG. 5 illustrates an example of a wireless device processing aspatially modulated packet 500, according to various embodiments. Asshown, packet 500 may comprises the following fields, as are typical ofa very high throughput (VHT) wireless LAN (WLAN) packet:

-   -   Legacy short training field (L-STF)    -   Legacy long training field (L-LTF)    -   Legacy signal field (L-SIG)    -   VHT signal field A1 (VHT-SIGA1)    -   VHT-SIGA2    -   VHT short training field (VHT-STF)    -   VHT long training field (VHT-LTF)    -   VHT-SIGB    -   Data Service Field    -   VHT Data    -   Padding and Tail

In general, the L-SFT, L-LFT, and L-SIG fields make up the legacypreamble of packet 500, the VHT-SIGA1, VHT-SIGA2, VHT-STF, VHT-LTF, andVHT-SIGB fields make up the VHT preamble of packet 500 and the remainingfields make up the data portion of packet 500.

When a device receives packet 500, it may perform the packet processingsteps 502 shown. Namely, the device may begin by employing its start ofpacket (SoP) detection and clear channel assessment (CCA) mechanisms.When the device receives packet 500, its SoP detection mechanism detectspacket 500. Next, the device may use its automatic gain control (AGC)and then apply its time and frequency recovery mechanism, to synchronizeits time and perform carrier frequency offset (CFO) correction.

In one embodiment, as shown, channel estimation is required at thereceiving device to be able to correctly decode the spatial domain.However, this information is always available in WLAN packets afterprocessing the legacy preamble. Therefore, the receiving device canexploit the spatial index at the preamble and can decide to process therest of the packet, if the packet is intended/destined for the device.For example, as shown, the device that received packet 500 may estimatethe channel to equalize the rest of the OFDM symbols. As would beappreciated, this is a relatively fast process that only requires thereceiving device to process the initial preamble fields of the packet.For example, preliminary testing has indicated that the channelestimation can be performed after only 16 μs.

To determine whether the device is the intended receiver of packet 500,it may compare the estimated channel to a locally-stored referencechannel associated with the device. If the estimated channel matchesthat of the reference of the receiving device, it may continue toperform the packet processing steps 502, such as demodulating the L-SIGfield of packet 500, demodulating the VHT-SIGA1 field of packet 500,demodulating the VHT-SIGA2 field of packet 500, etc. In other words, ifthe channel estimation indicates that packet 500 was intended for thereceiving device, it may continue to process and decode the remainder ofthe packet.

Conversely, if the estimated channel is not similar to that of thereference, this means that packet 500 was not intended/destined for thereceiving device. In various embodiments, when this happens, thereceiving device may forego decoding the entirety of packet 500. From aresource consumption standpoint, assume that the receiving device isable to perform the channel estimation from analyzing the preambleinformation within the timespan T_Preamble. Further, assume that fullprocessing of packet 500 will take T_packet amount of time to fullyprocess. By stopping further processing of packet 500 after determiningthat it was not intended for the receiving device, this results in aprocessing savings of T_packet−T_Preamble amount of time, which can bequite significant.

According to various embodiments, there are two alternative ways to savepower on the receiving device, when it determines that packet 500 wasnot intended/destined for it.

Under a first power saving mechanism, the receiving device may stilldecode the L-SIG symbol of packet 500. More specifically, once thereceiving device determines that the received packet 500 is not intendedfor the device, based on the detected transmit antenna index/channelestimation, it may still proceed to decode the L-SIG symbol of packet500. This provides the receiving device with the length of packet 500.In turn, in various embodiments, the device may turn off its radioreceiver for an amount of time that corresponds to the remaining lengthof packet 500. Under this approach, the energy savings will be:SavedEnergy=Pave×(T_VHTSIGA1/2+T_VHTSTF+n_VHTLTF×T_VHTLTF+T_VHTSIGB+T_ServiceField+T_DATA+T_PaddingTail)+P_host×(CRC+MAC_process)where Pave is the average power consumption of processing the packet andP_host is the power consumption in MAC layer.

By way of example, assume that an untended packet is a small packet with128 bytes payload size and MCS 0. Then, number of OFDM symbols,nSym=(Octet*8+16+6)/N dps where Octet=128 and N dbps=24 for 20 MHzchannel which results in nSym=44. This means that the radio of thereceiving device can be turned off for the following:4 μs×5+4 μs>44 (Data)=196 μs, plus skipping the process in MAC layer.

From the above, this means that the radio of the receiving device is onfor only 22 μs which results in a power savings of 89.9%.

In another embodiment, the receiving device may instead employ a powersaving mechanism that does not require decoding the L-LTF symbol ofpacket 500. In this embodiment, rather than calculating the length ofpacket 500 from its L-SIG symbol, the receiving device can alternativelysimply turn off its radio for a period of time based on the minimum sizeof packet 500. After this period of time elapses, the device may returnto its SoP detection state. Thus, the amount of energy that can be savedfrom this approach is as follows:SavedEnergy=Pave×(T_LSIG+T_VHTSIGA1/2+T_VHTSTF+n_VHTLTF×T_VHTLTF+T_VHTSIGB+T_ServiceField+T_PaddingTail)+P_host×(CRC+MAC_process)

Considering the same payload as in the previous example, the time thatthe radio of the device can be depowered is:4 μs×1 (L-SIG)+4 μs×5+4 μs×1 (Data)=28 μs plus skipping the process inMAC layer.

From the above, the radio of the device is on for 16 μs, which resultsin a power savings of 63.6%. Accordingly, the additional processing ofthe L-SIG symbol can actually reduce the amount of total power consumedby the device. However, either approach results in a fairly significantpower savings at the device.

Note that the power off times calculated above are based on the processin PHY. The time gap between packets, i.e., the shortest interframespaces (SIFSs) can be also considered which adds 16 μs to off time, in afurther embodiment.

As explained above, the receiving device requires channel stateinformation (CSI) to be able to correctly decode the spatial domain(e.g., the group address/antenna index). Notably, once the receivingdevice has performed its channel estimation from the preamble of areceived packet, it may compare this to a reference channel storedlocally that is associated with the device. This can be achieved in anumber of ways, according to various embodiments.

Although the changing of channels may not be fast in IoT applicationswhere the devices are not mobile, a mechanism is required for triggeringthe receiving device to update the reference channel. Typically, thedevice will have a channel update timeout based on the number ofreceived packets during a certain time interval. When the device is in apower save mode based on this proposed scheme, it can go back to itsnormal mode of operation when the number of received packets that areintended for the device does not reach a certain predefined count inthat time interface. This means that the reference channel of the deviceis outdated and needs to be updated.

Based on the detection methods detailed below, two types of referencechannel updates are possible, according to various embodiments, eitheror both of which can be selected, depending on the accuracy requirementsof the device.

In a first embodiment, each receiving device may be required to locallystore only a single reference channel associated with its assignedgroup/antenna index. In this case, the receiving device only needs tohave channel knowledge of its corresponding antenna and there is no needto estimate the entire channel matrix, making the computation fairlysimple. Under this scheme, the sender (e.g., an AP) is not required toapply any specific action/sounding and can keep sending spatiallymodulated packets via its antenna associated with the intended devicegrouping. In turn, when the channel is outdated, a receiving device maylisten to all packets transmitted by the sender and, once the devicereceives a packet intended for itself, it may save the channel stateinformation from that packet as the reference channel.

In a further embodiment, the receiving device may alternatively storechannel information for all channels used by the AP or other sender,which can provide for better accuracy. In this case, the AP or othersender sweeps its antennas when sending beacon packets to the variousreceiving devices. It will also add the index of the transmitted antennainside the beacon payload. In turn, all receiving devices that are in an‘update reference channel mode’ can determine the channels used by alltransmit antennas of the sender and store them to detect the spatialdomain (multicast address) of further packets.

Based on the two methods of channel updating described above, twodetection methods are also possible, in various embodiments. These twodetection approaches are illustrated in FIGS. 6A-6B, respectively.

In a first embodiment, as shown in example 600 in FIG. 6A, assume thatan AP 304 sends packets via its various antennas 410 to differentdevices 412 in the network, such as clients/devices 306 a and 306 b.Assume for purposes of illustration that antenna 410 a is associatedwith the grouping to which device 306 a belongs, that antenna 410 b isassociated with the grouping to which device 306 b belongs, and that theother antennas of AP 304, such as antenna 410 d shown, are associatedwith other spatial domains.

In the case shown, assume that each of devices 306 a-306 b store onlythe reference channels 604 associated with its respective devicegrouping. In such a case, the antenna index detection mechanism isrelatively simple. This simplicity comes from the fact that the APMsymbol (L-LTF) is known to the receiving device, meaning that thereceiving device 306 only needs to make a binary hypothesis test to beable to detect its own channel among the other channels with the highestprobability.

The OFDM based transmission of WLAN packets provides another dimensionto the detection, to increase the probability of detection which issubcarriers (frequency domain). By comparing the whole channelestimation vector (all subcarriers) to the reference channel vector, thereceiving device 306 can easily detect the spatial domain information ofthe received packet.

In some embodiments, the comparison between the received channelinformation 602 and the stored reference channel 604 on the receivingdevice 306 may entail evaluating the similarity of two complex vectors.For example, the receiving device 306 may compute the Pearson'sProduct-moment coefficient of the vectors, more commonly known as theircorrelation coefficient. This can be computed by dividing the covarianceof the two variables by the product of their standard deviations.

As would be appreciated, the absolute value of a correlation coefficientvaries between 0 and 1 and a larger value indicates greater similarity.In practice, a correlation coefficient of 0.9 or greater is large enoughto show that the channels are similar. However, when there issignificant correlation between transmit antennas and they are notspatially separated from each other, the correlation threshold should beadjusted very tight.

Using the above approach, each device 306 may compute the correlationcoefficient (con) between its estimated channel information 602 for areceived packet to its stored/reference channel information 604. Inturn, if the correlation coefficient exceeds a predefined threshold, thedevice 306 may continue to decode the remainder of the packet.Conversely, if the correlation coefficient is below the threshold, thedevice 306 may drop further processing of the packet. Thus, when device306 a receives a packet from antenna 410 a, it may determine that thepacket was intended for the device(s) in the device grouping to whichdevice 306 a was assigned and continue to process the packet. Similarly,when device 306 a receives a packet from antenna 410 b of AP 304, it maydetermine that the channel information of the packet is not correlatedto its stored reference channel information 604 and drop furtherprocessing of the packet. Device 306 b may take a similar approach, butonly process the full packets received from antenna 410 b of AP 304.

Referring now to FIG. 6B, another possible implementation entails eachof devices 306 a-306 b to store information 604 a for all channels usedby AP 304, not just its own reference. In this case, devices 306 may usea maximum likelihood detection approach and search over the differentEuclidean distances 616 between the received channel information 602 andits stored channel information 604 a, to determine whether the channelinformation 602 of the received packet matches that of its assignedchannel. In other words, the index of the antenna used to transmit thepacket, which is equivalently the destination grouping number/multicastaddress of the packet, is the reference channel 604 a with the minimumEuclidean distance 616 to the estimated channel 602.

For example, as shown, assume that device 306 a receives a packet fromantenna 410 a, which is associated with the device grouping to whichdevice 306 a belongs. If the reference channel 604 a stored by device306 a with the minimum distance to that of the packet is assigned todevice 306 a, it may continue to decode and process the remainder of thepacket. Conversely, assume that device 306 b also receives the samepacket. In this case, device 306 b may determine that the stored channel604 a with the shortest Euclidean distance 616 to that of the receivedpacket is associated with a spatial domain not assigned to the devicegrouping of device 306 b and, in turn, drop processing of the packet.

As would be appreciated, in addition to ceasing further decoding andprocessing of a packet not intended for the receiving device 306, thedevice may also depower (e.g., turn off) its radio receiver for anamount of time associated with either the remainder of the packet or fora time associated with the remainder of the packet up to a minimum sizeof the packet.

Various modifications are possible to the above approaches, in furtherembodiments. In another embodiment, generalized spatial modulation canbe used whereby a subset of the antennas of a sender are assigned to aparticular device grouping, as opposed to a single antenna. Althoughthis generalized approach requires more RF chains, with a maximum sizeof the antenna subsets, this also enables the sender to serve more thanNt groups of devices. Considering R-number of RF chains available attransmitter, the total number of groups that can be supported is:Total Number of Groups=C(Nt,R)+C(Nt,R−1)+ . . . +C(Nt,1)where C(k,n) is a k-combination of set size n.

In a further embodiment, the spatial modulation-based device groupingsintroduced herein can be used in conjunction with target wait time (TWT)feature of 802.11ax, where a group of stations are scheduled tolisten/transmit to reduce the power consumption. With the spatialmodulation antenna groupings, another level of grouping can be appliedon TWT to further reduce the power consumption of receiving devices, ifthe listen time intervals of TWT clients in a certain group areoverlapped. Then, the wait time of the network can be reduced to be ableto send immediate commands to devices and the increased powerconsumption from this change can be compensated by the antenna-aidedgrouping method.

In yet another embodiment, the above power saving approaches can also beused in combination with the upcoming 802.11ba standard for Low-PowerWake Up Radios (LP_WURs). In this case, all other unintended packetsduring the wake up interval of receiver are skipped, providing anotherlevel of power saving over the standard.

In another embodiment, while the spatial domain is used herein totransmit the multicast address/device grouping index to receivingdevices, the low complexity detection method detailed above can even beused when the sender only has a single antenna. In this case, thebenefit of using the proposed method is saving power by skipping furtherprocessing of unintended packets from other APs or clients.

In yet further embodiments, in addition to communicating the devicegrouping with spatial modulation, the grouping can also be combined withencoding the group number into the L-LTF by either 1.) making thedetection of the group ID more robust or 2.) expanding the number ofgroups by adding the LTF coding dimension with the spatial modulationdimension.

FIG. 7 illustrates an example simplified procedure for using spatialmodulation for power savings, in accordance with one or more embodimentsdescribed herein. For example, a non-generic, specifically configureddevice (e.g., device 200) may perform procedure 700 by executing storedinstructions (e.g., process 248). The procedure 700 may start at step705, and continues to step 710, where, as described in greater detailabove, the device may receive, at a wireless receiver of the device, apreamble of a spatially modulated packet. For example, the packet may bea WLAN packet and the preamble may include L-STF, L-LTF, and L-SIGsymbols/fields.

At step 715, as detailed above, the device may analyze the preamble ofthe packet to identify a transmit antenna index of the packet. To do so,in some embodiments, the device may estimate a channel from the preambleof the packet associated with the transmit antenna index. For example,the device may assess the L-LTF information from the preamble of thepacket, to estimate the channel of the packet.

At step 720, the device may determine that the packet was not destinedfor the device, based on the transmit antenna index of the packet, asdescribed in greater detail above. In some embodiments, the device maydo so by comparing an estimated channel of the packet to a referencechannel associated with the device. The device may store only thereference channel associated with its device grouping or, alternatively,all channels used by the sender of the packet. In the single referencechannel case, the device may store the reference channel based on thechannel used by a packet destined for the device. In the multiplereference channel case, the device may store channel informationobtained from beacons sent by the sender that indicate the channelinformation.

At step 725, as detailed above, the device may depowering, by the deviceand prior to decoding the complete packet, the wireless receiver of thedevice, based on the determination that the packet was not destined forthe device. In one embodiment, the device may do so by decoding a legacysignal (L-SIG) symbol of the packet to determine a length of the packetand computing an amount of time to depower the receiver based on thedetermined length of the packet (e.g., the remainder of the packet).Alternatively, the device may compute an amount of time to depower thereceiver based on a minimum size of the packet, without decoding theL-SIG of the packet. Procedure 700 then ends at step 730.

It should be noted that while certain steps within procedure 700 may beoptional as described above, the steps shown in FIG. 7 are merelyexamples for illustration, and certain other steps may be included orexcluded as desired. Further, while a particular order of the steps isshown, this ordering is merely illustrative, and any suitablearrangement of the steps may be utilized without departing from thescope of the embodiments herein.

The techniques described herein, therefore, help to reduce the resourceand power consumption of a device by using spatial modulation to denotethe intended receiver(s) of a packet. In doing so, the device canquickly assess the preamble of the packet and determine whether thepacket was intended for the device. If it is not, the device can skipfurther decoding and processing of the packet and depower its radioreceiver for a corresponding amount of time. For IoT device and otherreceiving devices with constrained resources, this approach can have aconsiderable effect on the battery lifespan of the device.

While there have been shown and described illustrative embodiments thatprovide for using spatial modulation to group devices, it is to beunderstood that various other adaptations and modifications may be madewithin the spirit and scope of the embodiments herein. For example,while certain protocols are shown, such as 802.11, other suitableprotocols may be used, accordingly.

The foregoing description has been directed to specific embodiments. Itwill be apparent, however, that other variations and modifications maybe made to the described embodiments, with the attainment of some or allof their advantages. For instance, it is expressly contemplated that thecomponents and/or elements described herein can be implemented assoftware being stored on a tangible (non-transitory) computer-readablemedium (e.g., disks/CDs/RAM/EEPROM/etc.) having program instructionsexecuting on a computer, hardware, firmware, or a combination thereof.Accordingly, this description is to be taken only by way of example andnot to otherwise limit the scope of the embodiments herein. Therefore,it is the object of the appended claims to cover all such variations andmodifications as come within the true spirit and scope of theembodiments herein.

What is claimed is:
 1. A method comprising: receiving, at a wirelessreceiver of a device in a network, a preamble of a spatially modulatedpacket; analyzing, by the device, the preamble of the packet to identifya transmit antenna index of the packet; determining, by the device, thatthe packet was not destined for the device, based on the transmitantenna index of the packet; and depowering, by the device and prior todecoding the complete packet, the wireless receiver of the device, basedon the determination that the packet was not destined for the device. 2.The method as in claim 1, wherein the transmit antenna index of thepacket is associated with one or more other devices in the network. 3.The method as in claim 1, wherein depowering, prior to decoding thecomplete packet, the wireless receiver of the device, based on thedetermination that the packet was not destined for the device,comprises: computing an amount of time to depower the receiver based ona minimum size of the packet.
 4. The method as in claim 1, whereindepowering, prior to decoding the complete packet, the wireless receiverof the device, based on the determination that the packet was notdestined for the device, comprises: decoding a legacy signal (L-SIG)symbol of the packet to determine a length of the packet; and computingan amount of time to depower the receiver based on the determined lengthof the packet.
 5. The method as in claim 1, wherein analyzing thepreamble of the packet to identify a transmit antenna index of thepacket comprises: estimating a channel from the preamble of the packetassociated with the transmit antenna index, and wherein determining thatthe packet was not destined for the device, based on the transmitantenna index of the packet, comprises: comparing the estimated channelto a reference channel associated with the device.
 6. The method as inclaim 5, further comprising: receiving, at the device, a beacon thatincludes channel information for the reference channel; and storing, bythe device, the reference channel based on channel information from thebeacon.
 7. The method as in claim 5, further comprising: receiving, atthe device, a packet destined for the device; and storing, by thedevice, the reference channel based on channel information from thepacket destined for the device.
 8. The method as in claim 1, wherein thewireless receiver of the device receives the packet during a target waittime (TWT) listen time interval.
 9. The method as in claim 1, whereinthe device receives the packet during an 802.11ba wake up interval ofthe device, and wherein the method further comprises: skipping, based onthe determination that the packet was not destined for the device,processing of further packets received by the device during the wakeupinterval of the device.
 10. The method as in claim 1, wherein the devicereceives the packet from a wireless access point with a single antenna.11. The method as in claim 1, wherein the device determines that thepacket was not destined for the device, based further in part on a groupidentifier encoded in a legacy long training field (L-LTF) of thepacket.
 12. An apparatus, comprising: one or more network interfaces tocommunicate with a network, wherein the one or more network interfacescomprise a wireless receiver; a processor coupled to the networkinterfaces and adapted to execute one or more processes; and a memoryconfigured to store a process executable by the processor, the processwhen executed configured to: receive, at the wireless receiver of theapparatus, a preamble of a spatially modulated packet; analyze thepreamble of the packet to identify a transmit antenna index of thepacket; determine that the packet was not destined for the apparatus,based on the transmit antenna index of the packet; and depower, prior todecoding the complete packet, the wireless receiver of the apparatus,based on the determination that the packet was not destined for theapparatus.
 13. The apparatus as in claim 12, wherein the transmitantenna index of the packet is associated with one or more other devicesin the network.
 14. The apparatus as in claim 12, wherein the apparatusdepowers, prior to decoding the complete packet, the wireless receiverof the apparatus, based on the determination that the packet was notdestined for the apparatus, by: computing an amount of time to depowerthe receiver based on a minimum size of the packet.
 15. The apparatus asin claim 12, wherein the apparatus depowers, prior to decoding thecomplete packet, the wireless receiver of the apparatus, based on thedetermination that the packet was not destined for the apparatus, by:decoding a legacy signal (L-SIG) symbol of the packet to determine alength of the packet; and computing an amount of time to depower thereceiver based on the determined length of the packet.
 16. The apparatusas in claim 12, wherein the apparatus analyzes the preamble of thepacket to identify a transmit antenna index of the packet by: estimatinga channel from the preamble of the packet associated with the transmitantenna index, and wherein the apparatus determines that the packet wasnot destined for the apparatus, based on the transmit antenna index ofthe packet, by: comparing the estimated channel to a reference channelassociated with the apparatus.
 17. The apparatus as in claim 16, whereinthe process when executed is further configured to: receive a beaconthat includes channel information for the reference channel; and storethe reference channel based on channel information from the beacon. 18.The apparatus as in claim 16, wherein the process when executed isfurther configured to: receive a packet destined for the device; andstore the reference channel based on channel information from the packetdestined for the apparatus.
 19. A tangible, non-transitory,computer-readable medium storing program instructions that cause adevice in a network to execute a process comprising: receiving, at awireless receiver of the device, a preamble of a spatially modulatedpacket; analyzing, by the device, the preamble of the packet to identifya transmit antenna index of the packet; determining, by the device, thatthe packet was not destined for the device, based on the transmitantenna index of the packet; and depowering, by the device and prior todecoding the complete packet, the wireless receiver of the device, basedon the determination that the packet was not destined for the device.20. The computer-readable medium as in claim 19, wherein the transmitantenna index of the packet is associated with one or more other devicesin the network.